This document discusses learner language and interlanguage. It defines interlanguage as the developing language system of second language learners. Learners create interlanguage rules from input and hypotheses, and their interlanguage changes over time as rules are added, altered, or deleted. Errors are an important part of interlanguage development and can indicate progress. The document also discusses factors like generalization, overgeneralization, transfer from L1, and developmental sequences that influence interlanguage.